The present invention relates to tape drive systems, and more particularly, this invention relates to a tape drive system with at least partially constrained tape-head contact.
Business, science and entertainment applications depend upon computing systems to process and record data. In these applications, large volumes of data are often stored or transferred to nonvolatile storage media, such as magnetic discs, magnetic tape cartridges, optical disk cartridges, floppy diskettes, or floptical diskettes. Typically, magnetic tape is the most economical, convenient, and secure means of storing or archiving data.
Storage technology is continually pushed to increase storage capacity and storage reliability. Improvement in data storage densities in magnetic storage media, for example, has resulted from improved medium materials, improved error correction techniques and decreased areal bit sizes. The data capacity of half-inch magnetic tape, for example, is currently measured in hundreds of gigabytes.
The current method of wrapping the tape over the head during tape drive operation does not in general allow constraining the contact between head and tape. In addition, it is well known that wrapped configurations may produce considerable effects. For example, spacing loss due to gap recession and debris accumulations on the head negatively affects performance. These debris accumulations can sometimes cause shorting of critical head elements. As tapes get smoother, stiction and running friction may become concerns. Another difficulty can be tape shifting and dynamic skew. Solutions such as coating tape heads may address one issue such as preventing shorting due to tape debris, but may cause increased susceptibility to stiction. There are no known solutions that improve upon all of these concerns.
An example of the current method of wrapping the tape over the head during tape drive operation is shown in FIG. 1, which illustrates a traditional flat-lapped bi-directional, two-module magnetic tape head 100, in accordance with the prior art. As shown, the head includes a pair of bases 102, each equipped with a module 104. The bases are typically “U-beams” that are adhesively coupled together. Each module 104 includes a substrate 104A and a closure 104B with readers and writers 106 situated therebetween. In use, a tape 108 is moved over the modules 104 along a tape bearing surface 109 in the manner shown for reading and writing data on the tape 108 using the readers and writers 106. Conventionally, a partial vacuum is formed between the tape 108 and the tape bearing surface 109 for maintaining the tape 108 in close proximity with the readers and writers 106.
Two common parameters are associated with heads of such design. One parameter includes the tape wrap angles αi, αo defined between the tape 108 and a plane 111 in which the upper surface of the tape bearing surface 109 resides. It should be noted that the tape wrap angles αi, αo includes an inner wrap angle αi which is often similar in degree to an external, or outer, wrap angle αo. The tape bearing surfaces 109 of the modules 104 are set at a predetermined angle from each other such that the desired inner wrap angle αi is achieved at the facing edges. Moreover, a tape bearing surface length 112 is defined as the distance (in the direction of tape travel) between edges of the tape bearing surface 109. The wrap angles αi, αo and tape bearing surface length 112 are often adjusted to deal with various operational aspects of heads such as that of FIG. 1, in a manner that will soon become apparent.
During use of the head of FIG. 1, various effects traditionally occur. FIG. 2A is an enlarged view of the area encircled in FIG. 1. FIG. 2A illustrates a first known effect associated with the use of the head 100 of FIG. 1. When the tape 108 moves across the head as shown, air is skived from below the tape 108 by a skiving edge 204 of the substrate 104A, and instead of the tape 108 lifting from the tape bearing surface 109 of the module (as intuitively it should), the reduced air pressure in the area between the tape 108 and the tape bearing surface 109 allows atmospheric pressure to urge the tape towards the tape bearing surface 109.
To obtain this desirable effect, the wrap angle αo is carefully selected. An illustrative wrap angle is about 0.8°±0.2. Note, however, that any wrap angle greater than 0° results in tents 202 being formed in the tape 108 on opposite edges of the tape bearing surface 109. This effect is a function of tape stiffness and tension. For given geometrical wrap angles for example, stiffer tapes will have larger tents 202.
If the wrap angle αi, αo is too high, the tape 108 will tend to lift from the tape bearing surface 109 in spite of the vacuum. The larger the wrap angle, the larger the tent 202, and consequently the more air is allowed to enter between the tape bearing surface 109 and tape 108. Ultimately, the forces (atmospheric pressure) urging the tape 108 towards the tape bearing surface 109 are overcome and the tape 108 becomes detached from the tape bearing surface 109.
If the wrap angle αi, αo is too small, the tape tends to exhibit tape lifting 205, or curling, along the side edge of the tape bearing surface 109 as a result of air leaking in at the edges and tape mechanical effects. This effect is shown in FIG. 2B. Particularly, the edges of the tape curl away from the tape bearing surface 109, resulting in edge loss or increased spacing between the edges of the tape and the tape bearing surface 109. This is undesirable, as data cannot reliably be written to the edges of a tape in a system subject to edge loss.
Additionally, the tape lifting 205 results in additional stress at points 206 which, in turn, may cause additional wear. Further augmenting such tape lifting 205 is the fact that the tape 108 naturally has upturned edges due to widespread use of technology applied in the video tape arts.
Beyond this relatively unconstrained head-tape contact, which is largely due to air skiving, the tape itself is unconstrained against lateral transient disturbances in the free span between tape guides where the head is located. These disturbances can produce mistracking between head and tape, and force, for example, cessation of the writing process.
Furthermore, other disturbances such as in tension can produce stick-slip conditions, mistracking and head-tape-spacing modulation.